1. Field of the Invention
This invention pertains to formed blocks or piles of concrete or other material for use as structural units in the construction of a variety of shore-protective works, among other applications. This invention is further directed to offshore breakwaters and like structures that are built by laying a multiplicity of such blocks into one or more layers and which function to control the processes of erosion and accretion, thereby contributing to coastal protection.
2. Description of the Prior Art
Coastal engineers have expended much effort for the development of measures truly effective to prevent the wave-induced erosion of beaches and shorelines. Yet various existing types of breakwaters, for example, seem to have some weakness or other. I myself have recently witnessed a sand-cored, concrete breakwater which had collapsed overnight as a result of action by tidal waves. This accident was obviously due to the undermining of the rigid and impervious breakwater by the tidal waves, resulting in the outflow of the core sand and in the consequent breakdown of the concrete top and side slopes.
Also responsible for the collapse of the breakwater in question was the great vertical load that had been exerted on the seabed by the breakwater itself. Since the breakwater had its understructure buried relatively deep into the seabed, it has presumably blocked the flow of underground water under its own weight. The tidal waves, however, forced the underground water to flow and thus caused the outflow of the core sand.
The tetrapod, a cast concrete form with four symmetrically spaced legs, represents another example of prior art pertinent to my invention. Although tetrapods can dissipate and damp wave action, they do, however, have certain disadvantages, one of these being their vulnerability to fracture. As an additional disadvantage, any aggregate of tetrapods imposes a considerable vertical load upon its foundation, possibly causing the same to sink.